Xeroderma pigmentosa is a rare condition passed down through families in which the skin and tissue covering the eye are extremely sensitive to ultraviolet light.

Causes, incidence, and risk factors:

Ultraviolet light -- such as that found in sunlight -- damages the genetic material (DNA) in skin cells. Normally, the body repairs this damage. But in persons with xeroderma pigmentosa, the body does not fix the damage. As a result, the skin gets very thin and patches of varying color (splotchy pigmentation) appear.

The condition also causes spidery blood vessels in the skin (telangiectasia ) and skin cancer. Skin cancer often occurs before the child is 5 years old.